import os
from collections import OrderedDict
import panel as pn

path = os.getcwd()

down = '│'
right = '└──'

def expand_dir(event):
    """For a dir - populate with subdirs"""
    def has_children(parent):
        return os.path.isdir(parent)

    def get_children(parent):
        return sorted(os.listdir(got))

    def populate_value(parent, child):
        return os.path.join(parent, child)

    got = event.new[0]
    obj = event.obj
    old = list(event.obj.options.items())
    name = next(k for k, v in old if v == got)
    index = next(i for i, (k, v) in enumerate(old) if v == got)
    if right in name:
        prefix = f'{name.split(right)[0]}{down} {right}'
    else:
        prefix = right

    if has_children(got):
        items = get_children(got)
        for i, item in enumerate(items):
            value = populate_value(got, item)
            old.insert(index+i+1, (f'{prefix} {item}', value))
    event.obj.options = dict(old)

items = [p for p in sorted(os.listdir(path)) if not p.startswith('.')]
options = OrderedDict(zip(items, (os.path.join(path, item) for item in items)))
select = pn.widgets.MultiSelect(options=options, size=14)
select.param.watch(expand_dir, 'value')

row = pn.Row(select)
row.servable()